The present invention relates to a pattern formation method whereby a resist pattern is formed on a semiconductor substrate in the process of manufacturing semiconductor devices and to a surface treating agent for use in the process of forming the resist pattern.
As higher-density and higher-integration semiconductor devices have been implemented in recent years, there has been increasing demand for micro-fabrication technology.
As a first method of enabling micro-fabrication in a lithographic process, there has been developed a technique for forming a resist pattern from a chemically amplified resist which utilizes the generation of an acid in response to exposing radiation such as a DUV ray from the light source of an excimer laser or a ray of a shorter wavelength such as an electron beam or an x-ray.
Referring now to FIGS. 12 and 13, a pattern formation. method using a chemically amplified resist will be described as a first conventional embodiment.
FIG. 12 shows the process flow of the pattern formation method according to the first conventional embodiment. FIG. 13 shows a surface of a semiconductor substrate formed by the pattern formation method according to the first conventional embodiment.
First, hexamethyldisilazane (hereinafter referred to as HMDS) as a surface treating agent is supplied to the surface of the semiconductor substrate 1 made of silicon to render the surface of the semiconductor substrate 1 hydrophobic and thereby improve adhesion to the semiconductor substrate 1. The process is performed by bubbling liquid HMDS with the use of a nitrogen gas and spraying HMDS to the surface of the semiconductor substrate 1 heated to 60.degree. C. for 30 seconds, as shown in FIG. 13(a). During the process, Si(CH.sub.3).sub.3 (trimethylsilyl group) is substituted for the hydrogen atom of an OH group on the surface of the semiconductor substrate 1 as shown in FIG. 13(b), so that the surface of the semiconductor substrate 1 becomes hydrophobic and adhesion to the semiconductor substrate 1 is thereby improved, while NH.sub.3 (ammonia) is generated.
Next, a resist film is formed by coating the surface of the semiconductor substrate with a chemically amplified resist. The resist film is then exposed to light using a desired mask and sequentially subjected to post-exposure bake (hereinafter referred to as PEB) and development, resulting in a resist pattern.
As a second method of enabling micro-fabrication in a lithographic process, there has been proposed a technique for improving the adhesion of a resist pattern to a semiconductor substrate, as disclosed in Japanese Laid-Open Patent Publication SHO 58-188132.
Below, a pattern formation method using a resist containing, e.g., a phenol-based resin will be described as a second conventional embodiment.
First, a surface treating agent containing a silane compound represented by the following general formula: EQU R.sup.1 SiX.sub.3-n R.sup.2.sub.n
(wherein n represents 0, 1, or 2; X represents a halogen group or --OR' group (R' represents an alkyl group having 1 to 3 carbons); R.sup.1 represents a group containing CH.sub.2 .dbd.CH--, ZCH.sub.2 -- (Z represents a halogen group), or ##STR1## and R.sup.2 represents a hydrogen or an alkyl group having 1 to 3 carbons) is supplied to a surface of a semiconductor substrate made of silicon to render the surface of the semiconductor substrate hydrophobic and thereby improve adhesion to the semiconductor substrate.
Next, a resist containing, e.g., a phenol resin is applied to the surface of the semiconductor substrate to form a resist film, which is then exposed to light using a desired mask and sequentially subjected to PEB and development, resulting in a resist pattern.
FIGS. 14 and 15 show schematic cross-sectional configurations of a resist pattern 2 formed on the semiconductor substrate 1 made of silicon or on a semiconductor substrate 5 made of BPSG by the pattern formation method according to the first conventional embodiment. Specifically, FIGS. 14 and 15 show the cross-sectional configurations of patterns with 0.25-.mu.m lines and spaces obtained by coating the surface of the semiconductor substrate 1 made of silicon or the semiconductor substrate 5 made of BPSG with a positive chemically amplified resist (KRF K2G commercially available from Japan Synthetic Rubber Co., Ltd.) having a thickness of 0.7 .mu.m, exposing the resist to light by a KrF excimer laser stepper having a numerical aperture of 0.5, performing PEB with respect to the resist at a temperature of 100.degree. C. for 90 seconds, and developing the resist in a 2.38 wt % aqueous solution of tetramethylammonium hydroxide.
In the first conventional embodiment, an insoluble skin layer 3 is formed on the surface of the resist pattern 2 as shown in FIG. 14 or a footing 4 is formed at the base of the resist pattern 2 as shown in FIG. 15. The formation of the insoluble skin layer 3 on the surface of the resist pattern 2 or the formation of the footing 4 at the base of the resist pattern 2 may be attributed to different atmospheres or different states on the surface of the substrate in which the pattern is formed.
The insoluble skin layer 3 formed on the surface of the resist pattern 2 or the footing 4 formed at the base of the resist pattern 2 will adversely affect the subsequent process, resulting in a first problem of a reduction in the yield of semiconductor devices.
On the other hand, a second problem of unsatisfactory adhesion occurs in the case of performing micro-fabrication with respect to a single layer during the lithographic process, though the resist pattern formed on the semiconductor substrate by the pattern formation method according to the second conventional embodiment exhibits improved adhesion that has been previously unattainable to the semiconductor substrate since the surface of the semiconductor substrate has been treated with the above surface treating agent. As a result, peeling off may occur when a pattern with a line width of 0.30-.mu.m or less is formed by exposure to an i line, when a pattern with a line width of 0.25-.mu.m or less is formed by exposure to a KrF excimer laser, or when a pattern with a line width of 0.20-.mu.m or less is formed by exposure to an ArF excimer laser.